Migrate solution to .NET 10 (update SDK, projects and generated reference assemblies)

[Vake93]

Motivation

• Move the solution and its tooling from .NET 5 to .NET 10 to use the newer SDK and updated reference assemblies.
• Regenerate reference assembly resources and targets for net10.0/aspnet10.0 so the internal compilation/emit tooling targets the newer frameworks.

Description

• Update the global SDK to 10.0.100 in global.json and add LangVersion in src/Directory.Build.props.
• Change project TargetFramework values from net5.0 to net10.0 across library, build and test projects and bump affected package versions (for example Microsoft.CodeAnalysis.CSharp to 4.14.0 and Microsoft.AspNetCore.TestHost to 10.0.0).
• Replace generated reference assembly sources and MSBuild target files by renaming Net50/AspNet50 resources to Net10/AspNet10 and add Generated.Net10.targets / Generated.AspNet10.targets, removing the old net5 generated targets.
• Update internal tooling and code paths to use the new frameworks, including TargetFrameworks constants, NuGetClient.frameworkName, BuildService target framework selection, and the Generate.ps1 script that produces the generated files; update readme.md to reference .NET 10.
• Note: HttpMethodAttribute initialization was changed in HttpMethodAttribute.cs (the HttpMethods initializer was modified).

Testing

• Performed dotnet restore and dotnet build against the updated SDK and the solution built successfully.
• Executed the unit test suite via dotnet test for the Express.Net.Test project and all tests completed successfully.
• Verified the reference-assembly compilation tests (Net10Compilation and AspNet10Compilation) compile and emit without diagnostics.
• Package restore of generated reference assemblies completed successfully during the test/build steps.

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Codex Task